Fr Magill told mourners that our political leaders needed to work together again so that our young people can "have a life, not a gun put in their hands".
He commended the coming together of nationalist and unionist leaders in Creggan for a vigil less than 24 hours after the murder but demanded to know why it took "the death of a woman with her whole life in front of her" to get to that point.
His strong words brought the congregation - including Prime Minister Theresa May, Taoiseach Leo Varadkar, Irish President Michael D Higgins, Sinn Fein's Mary Lou McDonald and Michelle O'Neill, and the DUP's Arlene Foster - to their feet in a standing ovation.